Probing: Add support for exponential startup probing

webrtc/modules/remote_bitrate_estimator/aimd_rate_control.cc

 /*
  *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 112 matching lines @@
     current_input_ = *input;
   }
 }
 
 void AimdRateControl::SetEstimate(int bitrate_bps, int64_t now_ms) {
   updated_ = true;
   bitrate_is_initialized_ = true;
   current_bitrate_bps_ = ChangeBitrate(bitrate_bps, bitrate_bps, now_ms);
 }
 
-uint32_t AimdRateControl::ChangeBitrate(uint32_t current_bitrate_bps,
-                                        uint32_t incoming_bitrate_bps,
+uint32_t AimdRateControl::ChangeBitrate(int current_bitrate_bps,
+                                        int incoming_bitrate_bps,
                                         int64_t now_ms) {
   if (!updated_) {
     return current_bitrate_bps_;
   }
   // An over-use should always trigger us to reduce the bitrate, even though
   // we have not yet established our first estimate. By acting on the over-use,
   // we will end up with a valid estimate.
   if (!bitrate_is_initialized_ && current_input_.bw_state != kBwOverusing)
     return current_bitrate_bps_;
   updated_ = false;
@@ skipping 154 matching lines @@
 }
 
 void AimdRateControl::ChangeRegion(RateControlRegion region) {
   rate_control_region_ = region;
 }
 
 void AimdRateControl::ChangeState(RateControlState new_state) {
   rate_control_state_ = new_state;
 }
 }  // namespace webrtc